When it comes to pruning trees, just a little off the sides will do

It's time to prune most summer-flowering trees such as crape myrtle, vitex, pomegranate, althea and mimosa. Pruning should generally be done between late January through early March to enhance their natural shape while correcting any problems.

View full sizeHarsh pruning of crape myrtles is not healthy for the trees, contrary to popular belief. It leaves them structurally weak and more susceptible to fungus diseases such as powdery mildew and insects. One of the most abused trees in Louisiana's residential and commercial landscapes is the crape myrtle. Crape myrtles need occasional pruning to obtain the desired landscape effect, but many times these plants are butchered for no good reason.

An unfortunate trend is to cut back the tops, which results in a tree reduced to large branches ending in stubs. The term coined for this is "crape murder."

The lush growth that occurs at these cut sites appears vigorous, but is actually structurally weak and is more susceptible to fungus diseases such as powdery mildew and insects. And when pruning is conducted improperly over several seasons, unsightly large, swollen knobs form at the point where pruning is done.

Horticulturists and landscape architects across the Southeast are appalled that this method of pruning continues to increase. There is not another small flowering tree used in Louisiana landscapes that is treated this way. Why should we do it to crape myrtles?

Pruning myths

I often encounter gardeners who have somehow gotten the idea that they are supposed to prune their crape myrtles that way -- generally from seeing that someone else has done it. Nothing could be farther from the truth. Enhancing the natural shape of our crape myrtles is the most appropriate way to maintain them.

Some gardeners have been told that crape myrtles need to be pruned radically to bloom well. This is inaccurate. The flower clusters can be larger on these trees, but the added weight on the ends of long branches causes them to bend over awkwardly, especially after it rains. And since the tree is smaller, fewer flower clusters are produced.

Sometimes crape myrtles are pruned improperly in an effort to create a different shape. A wide variety of crape myrtle cultivars are available today, and as you look around area landscapes you will see great diversity among them.

Some grow tall and upright like a vase, while others are shorter and spreading, more like a mushroom. You cannot make an upright-growing crape myrtle grow in the shape of a mushroom by cutting it back. The new growth will simply grow upright again over time.

So, if you want a crape myrtle that will mature into the shape you desire, make sure you choose one that grows that way naturally.

Sometimes young crape myrtles are cut back to make them look fuller. Young trees often appear more spindly and less substantial, but this is a matter of age, not something that needs to be corrected with pruning. Over time, young trees will attain the shapely, full canopies of older trees without drastic pruning.

I also hear people say they need to cut their crape myrtles back because of their size. If the height of the crape myrtle is not causing a problem with a nearby structure or power lines, there is little reason to reduce a tree's height. They are indeed trees, and they are supposed to be relatively large.

The right way to prune

To prune a crape myrtle properly, first have a specific, valid purpose in mind. In other words, if you can't come up with a good reason to prune your tree, leave it alone.

If you do see something that calls for pruning, study the tree carefully and determine what needs to be pruned to accomplish the specific purpose identified.

Every crape myrtle will need some pruning in its life to grow properly and fit in well with its surroundings. Here are some examples:

One important reason to prune is to eliminate crossed and rubbing branches, as rubbing branches can lead to open wounds.

Over time, branches that are too low on the trunk will need to be pruned to raise the canopy. We often need to remove weak, thin branches from the inner part of the tree to produce a cleaner-looking tree.

Selected branches may need to be pruned back to a side branch or the trunk to create a shapelier tree. Generally, avoid cutting back or shortening branches much thicker than your finger, although cutting larger branches back to a side branch or to the trunk when needed is fine.

Of course, you need to prune to keep suckers removed from the base of the trunk. Cut suckers flush with their point of origin, and then spray the area with a sucker-suppressing product. This will keep suckers from growing back for a year or more. Check local nurseries for availability. One product, Sucker Stopper, is readily available online.

You may also need to redirect the direction of a branch's growth. This can be done by studying the branch carefully, and looking for a side branch that grows in the desired direction. Prune back to that branch, and you have redirected the growth of the branch. This can be helpful where trees are too close to a structure, such as a house. Branches can be redirected to grow away from or up and over the roof line.

With its smooth, muscular trunks, peeling bark, filigree of leafless branches in the winter and exceptionally long blooming season in summer, the crape myrtle is rightfully popular here. Make sure you keep yours looking its best.

DAN GILL'S MAILBOX

Do leftover fertilizers lose their effectiveness from one year to the next? How about pesticides such as herbicides, insecticides and fungicides?

C. Kathy Washington

Fertilizers retain their effectiveness indefinitely, as long as they are kept dry. Dry fertilizers, such as granular formulations or soluble powders, will absorb moisture from the air, and should be stored in sealed plastic bags or containers. Dry pesticide formulations, such as dusts or wettable powders, stay potent for several years if kept dry. Use baits within one year. Liquid pesticides should be used up the first year or two after opening them, as they will lose potency over time. For that reason, I always recommend that gardeners buy the smallest container of a pesticide that is available. Also, before you buy a pesticide, see if something you already have on hand will do the job. Most of us have far too many partially used bottles of pesticides hanging around. Remember to always keep fertilizers and pesticides stored safely. If you have young children, that means under lock and key.

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Please identify the black stuff and white dots on my Savannah holly trees, and tell me how I can treat them.

Chuck Manders

The main problem is the white dots, which are insects called Florida wax scale. Scale insects settle into one spot, stick their needle-like mouth parts into the leaf to feed on sap and never move again. They are also often covered by a waxy coating that makes them difficult to control with contact insecticides. The black stuff is sooty mold, a fungus that grows on the sugary excretions of the scale insects. Sooty mold does not attack the plant, and will eventually disappear if the scales are controlled. This is an excellent time of year to treat for scale. Low-toxicity horticultural oil sprays are quite effective. Stop by your local nursery and pick up any of several brand names, such as Year Round Spray Oil, Volck Oil and others, and use them according to label directions. Make two to three applications about two weeks apart. The dead scale insects and sooty mold may not fall from the tree immediately, so don't be alarmed if you still see them after your third spray. If it is not practical to spray the trees, you can treat them with a systemic insecticide called imidacloprid applied to the roots. Look for brands like Bayer Tree and Shrub Insect Control with Merit and follow label directions carefully.

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We have four 20-year-old crape myrtles about 30 feet tall. They have not looked good for the last couple of years. They did not produce very many blooms last year. I have asked around for pruning suggestions in hopes of giving them some new growth. I received two opinions. Selectively prune the sickly branches (most of them look sickly to me) or cut the top third of the trees off. What is your opinion?

George A. Strain

There is a misconception that pruning crape myrtles can somehow make a sickly tree healthy. Pruning a tree will not take away the reasons that caused it to look sickly to begin with. Those reasons could include age, stress, insect problems, root damage, disease problems and shade from other trees. If a tree is sickly before it's pruned, when it grows back out it will likely still look sickly. And, if the trees are not healthy to begin with, cutting off sections of them could make them even less happy. If you cut them back hard, all you will do is ruin their shape. I do not see pruning as a solution to your problem. Try fertilizing them. Providing added nutrients is about the best tool we have to improve a plant's vigor. Fertilize this month or next; you can use any of a number of techniques, but you might find tree spikes the easiest to apply. These are generally available at area nurseries. Follow package directions. If you like, take some pictures of the trees in June or July, when crape myrtles are generally looking good, and send them to me. Perhaps I can help you determine why they are doing poorly if I can see what you are seeing.